1. Field of the Invention
The present invention relates to a light-tight cassette or magazine (hereinafter called "cassette") for holding a roll of light-sensitive photographic material.
The invention is particularly suitable for embodiment in a cassette for holding and dispensing a roll of photographic material for use in phototype-setting apparatus.
2. Description of the Art
Cassettes in the form of a rectanguloid box having a peripheral light-tight slot via which light-sensitive material can be drawn from a roll located in the box are known. The light-tightness of the dispensing slot is important for preventing light from entering the cassette and fogging outer convolutions of the roll of light-sensitive material when the cassette is removed from its wrapper and during day-light loading or unloading of the cassette into or from a photographic exposure apparatus.
Most present-day cassettes are made from plastics or cardboard and they are cheap to manufacture, are light in weight, and are easy to handle. The peripheral wall or shell of the cassette has in-turned lips forming the dispensing slot and light-tight sealing of this slot is effected by elastically deformable strips, e.g. strips of velvet. Provided that the length of the cassette is not too great, the sealing strips can be sufficiently elastically deformable by the pressure exerted by the light-sensitive material in the slot to compensate for any deformation of either of the shell lips which may occur, e.g. when photographic material is being pulled through the slot. Generally speaking, this compensation is capable of ensuring effective light-tightness of cassettes up to about 10 inches in length. At one time rolls of photographic material wider than 10 inches were not in common use but modern phototypesetting apparatus use wider photographic materials. Rolls between 10 and 13 inches in width are now often used and the trend is towards widths up to 20 inches. Practice shows that it is extremely difficult to produce cassettes with a dispensing slot 10 to 13" in length with lips which are sufficiently rigid to resist bending under forces to which they are subjected during ordinary use.
One reason why lip bending occurs is that when photographic material is withdrawn from the cassette it is forced to change direction on emergence from the dispensing slot. A component of force normal to the plane of the material in the slot is therefore exerted on one of the slot lips which tends to displace it away from the opposite lip.
Another cause of lip bending is careless handling of the cassette by the operator during removal of a sealing tape that is stuck over the dispensing slot of a new cassette. Usually one lip only of a cassette is prone to easy deformation and no harm is done if the sealing tape is pulled off the cassette in the direction towards the opposite lip. However, if the tape is pulled off in the other direction the less rigid lip can be deformed sufficiently to allow light to enter the cassette and cause fogging of the light-sensitive material.
Commonly used strips of velvet or the like for light-tightly sealing the dispensing slot can compensate for lip deflections of, say, maximum 1 mm, but experience shows that this maximum value is easily exceeded in the case of cassettes longer than 12 inches.
It is known to increase the stiffness of a lip of a dispensing slot by folding or flaring an inner portion of the lip backwardly or outwardly to form a flange which is connected to the adjacent interior wall of the shell thereby to form a kind of hollow beam or tube (see e.g. DE-A-27 45 031). The bending resistance of the lip achieved in this way depends of course on the width and orientation of the flange. For such a stiffening flange to be reliable in the case of a cassette having a length of 12 inches or more, the flange would require to be of such width as to impose undesirable limitations on the choice of the slot location and orientation. In order to be compatible with certain currently marketed exposure apparatus, the cassettes from which the light-sensitive material is dispensed must have a dispensing slot located with its exit mouth very close to, e.g. 10 mm or less from, the plane of one of the side walls of the cassette, i.e., at a corner. When taking account of the most suitable orientations of the plane of the slot for avoiding awkward changes of direction of the light-sensitive material on arrival at the entrance to the dispensing slot within the cassette, this means that one lip of the dispensing slot has to be at a relatively small angle (an angle that may be less than 15.degree.) to the adjacent side wall of the cassette shell. That is why most cassettes for phototypesetting photographic material have a dispensing slot with its exit mouth near a corner of the cassette shell and its lips orientated asymmetrically between the adjacent side walls of the shell. The slot lip which is at the smaller angle to its adjacent side wall is more susceptible to bending than the other lip. And obviously the closeness of that weaker lip to the cassette shell limits the width of stiffening flange which could be accommodated.
It is an object of the present invention to impart to a dispensing slot lip of a cassette for holding a roll of wide photographic material to be given an enhanced bending resistance while at the same time allowing the lip to be located close and at a small angle to an adjacent side of the cassette as above referred to.